Typically, there has been used a furnace having a multilayered refractory structure, in which a refractory such as firebricks is laid in layers on the inner side of an iron outer shell (furnace shell) so that the furnace exhibits resistance to an intense heat therein.
Such a furnace having a multilayered refractory structure has been used as a blast furnace, a non-ferrous furnace, a glass furnace, a hot-blast furnace for supplying hot blast to these furnaces, an annealing furnace of continuous processing equipment for a thin plate, or a heating furnace for heating various steel materials.
As an example of a furnace having a multilayered refractory structure, description will be made on a hot-blast furnace for supplying hot blast to a blast furnace.
A hot-blast furnace includes an internal-combustion hot-blast furnace and an external-combustion hot-blast furnace. An internal-combustion hot-blast furnace has a combustion portion and a heat-storage portion integrally housed therein (e.g., Patent Literature 1). An external-combustion hot-blast furnace has separate furnace bodies respectively functioning as a combustion portion and a heat-storage portion, which are connected to each other at their upper ends via a connection pipe (e.g., Patent Literature 2 and Patent Literature 3).
In either type, combustion gas having a high temperature is generated in the combustion portion with the assistance of a burner, and is passed through the heat-storage portion to store heat. When a sufficient amount of heat is stored, air is reversely passed through the heat-storage portion, thereby generating hot blast (e.g., Patent Literature 4).
The furnace wall of the hot-blast furnace is formed by laying a refractory such as firebricks on the inner side of an iron outer shell (furnace shell) so that the furnace wall exhibits resistance to an intense heat therein. The firebricks of the furnace wall are laid in layers toward a furnace core, so that the thickness of the furnace wall is increased to ensure a heat resistance for a specific part. Other refractories used for the furnace wall are heat-insulating bricks or boards laid between the firebricks and the furnace shell and a heat-insulating coating material sprayed onto the inner surface of the furnace wall.
In an internal-combustion hot-blast furnace, the combustion portion and the heat-storage portion are surrounded by the furnace wall formed as described above. A partition formed of a refractory is provided between the combustion portion and the heat-storage portion.
In an external-combustion hot-blast furnace, each of the furnace bodies respectively functioning as the combustion portion and the heat-storage portion is provided with the above furnace wall having refractories.
Heat-storage bricks as a heat-storage refractory are filled in the heat-storage portion of the internal-combustion hot-blast furnace or in the furnace body as the heat-storage portion of the external-combustion hot-blast furnace. Such heat-storage bricks, being characterized by having pores and a large heat capacity, are a refractory basically similar to firebricks, and are exemplified by hexagonal-columnar gitter bricks (e.g., Patent Literature 5).
A hot-blast furnace is intended to have a decades-long durability. However, since the operation of the hot-blast furnace is accompanied by deterioration of the refractories therein, the hot-blast furnace requires dismantling of the worn refractories therein for renewal thereof. Refractories to be dismantled include the refractories used for the furnace wall and the partition (if the furnace is an inner-combustion type) and the refractory used as the heat-storage material. A large-scale operation using heavy equipment is necessary for dismantling these refractories.